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Build an Efficient HF Mobile Antenna

Continued from page 46

lay the wire straight out into a yard. If it does have kinks in it, remove them by tying one end of the wire to a fence posi and giving the other end a few good yanks. The 11 taps are located at the bottom end of ihe coil form where it attaches to the mast. Each tap is staggered from the other by approximately an inch so they donTi end up bunched up on top of each other. Before worrying with the taps, compleie the coil winding and use epoxy lo secure all but the bottom 11 windings. After the epoxy cures (overnight!) unwind the unsecured windings. Scrape the enamel completely from a 1" length of wire an J bend it down on top of itself to form a closed loop about 0.25" long. We want the copper in the loop to be bright and shiny because we will later fill the loop w ith solder When done, secure the lapped windings with epoxy.

Leave enough w irc at the end to install the lai^ge solder lug that will be screwed down against the #10-32 stainless steel through-bolt we will install! at the Lop of the mast. This through-bolt is the only mechanical conncc-■ion in ihe antenna functioning as an electrical termination. Jt ties ihe bottom of the coil to the end of the copper braid from the top of the mast, and is required to allow removal of the resonator, h uses a wingnut fastener An additional length of wire from the solder lug is bent back up the coil form and soldered to the desired coil tap. This is a semi-permanent connection so, before final assembly, make sure it is in the frequency range you will be using. 1 don't recommcnd alligator clips, sliding contacts, or miniature banana plugs; a soldered connection will ouiperlbrm all of these alternatives-

Glue another 1.5" PVC coupling sleeve into the top end of the coil form, Self-uipping sheet metal screws secure the copper top hat and whip mount into the sleeve. The top hat and whip mount are made from V-long 1.5"-diameter copper pipe and pipe cap. Drill the pipe cap in the exact center of its top, and install a bolt here that matches the size and tread requirements of your spring loaded whip. Drill additional holes around the pipe and cap assembly at 90-degree intervals. Insert two lengths of #10 solid copper wire 21" long through these holes and center them on the assembly. Then, using a torch, solder the entire assembly. Don't try to solder just a portion of the assembly; copper is too good a conductor of heat to allowr thai. All connections will have be soldered at the same lime. The top wire from the resonator coil is also soldered to this assembly. The wire can be kept in place by wrapping it around one of the top hat radials prior to soldering. All soldering should be done prior to installing the assembly into ihe PVC coupling.

40 Meters

See Figure 3, The 40 meter resonator is built like the 75 meter resonator The minimum required coil form length is eight inches. Space-wind a total of 44 turns of #12 bare copper wire onto the form and secure it with epoxy, Approximately 33 feet of wire is required. The same nylon spacing twine used on the 75 meter coil can be used here, but a crossed-wire top hat is not used. Otherwise, the whip mounting is the same as on the 75 meter resonator. The 40 meter coil becomes resonant at 7254 kHz with the bottom two turns shorted. Each turn of the coil shifts the resonant frequency by about 200 kHz. The

Photo C. 20 meter resonator mounted on the mobile mast.

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